# [ANSYS Meshing] Hot to change the O grid in the following pipe

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May 3, 2013, 02:11
Hot to change the O grid in the following pipe
#1
Senior Member

p ding
Join Date: Mar 2009
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Dear friends:
I use O grid to generate mesh for a ellipse pipe, i not want to change the rectangular edge in the center of the pipe to a circle so as o further improve the quality of mesh.
but how to change the edge in to a circle?
Regards
Attached Images
 screen.jpg (57.7 KB, 43 views)

 May 3, 2013, 02:42 #2 Senior Member   Javi Join Date: Jan 2013 Posts: 260 Rep Power: 8 I donīt understand what you mean. Do you want to adecuate the edges to your geometry? You can edit the edge so you get a edge with the same shape. Blocking -> Edit edge -> Split Edge -> Automatic Linear. Then select the edge you want and you get the same shape of the curve. If you want to use "Automatic linear" you have to "update" before.

 May 3, 2013, 03:04 #3 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 19 Do you want the inner block to be a cylinder? If so, don't do it. It degrades the mesh at the points of intersection of the edges. That's why you use an O-grid at all - to blend from the outer circle to an inner rectangle. __________________ The skeleton ran out of shampoo in the shower.

May 3, 2013, 05:56
#4
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p ding
Join Date: Mar 2009
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Quote:
 Originally Posted by RodriguezFatz Do you want the inner block to be a cylinder? If so, don't do it. It degrades the mesh at the points of intersection of the edges. That's why you use an O-grid at all - to blend from the outer circle to an inner rectangle.
yes, i want the inner block to be a cylinder. but i think if it is a cylinder, then we can use a cylindrical coordinate mesh , it is orthogonal. why you say it degrades the mesh?
thank you

 May 3, 2013, 06:01 #5 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 19 Maybe I don't get you right, but can you draw a simple sketch, how you want the mesh to look like at the face? good: good.jpg bad: (not all lines are drawn) bad.jpg bad, too: bad2.jpg __________________ The skeleton ran out of shampoo in the shower.

May 3, 2013, 08:49
#6
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p ding
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Quote:
 Originally Posted by RodriguezFatz Maybe I don't get you right, but can you draw a simple sketch, how you want the mesh to look like at the face? good: Attachment 21431 bad: (not all lines are drawn) Attachment 21432 bad, too: Attachment 21433
Dear friends:
I merge the four vertices of the inner block, then i get this . but the vertice is not at the center position.
Attached Images
 2013-5-3 20-48-36.jpg (99.4 KB, 33 views)

 May 3, 2013, 09:10 #7 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 19 But how do the center cells looks like? It is exactly the same bad shape as in my second "bad"-case: distorted triangles. This isn't hexa any longer and also for tri mesh it would be bad! __________________ The skeleton ran out of shampoo in the shower.

May 3, 2013, 16:01
#8
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Javi
Join Date: Jan 2013
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If you do exactly you said before you get this picture. Iīve moved the vertex to the center of the cylinder and I get this. But...as Phillip said before... you get bad quality elements as you can see in the quality histogram.
Attached Images
 1.jpg (86.7 KB, 30 views) 2.jpg (49.1 KB, 24 views)

 May 6, 2013, 03:26 #9 Senior Member   Javi Join Date: Jan 2013 Posts: 260 Rep Power: 8 I would like to know how to do this but with mesh mix. I mean, with hexas and in the center of the cylinder with tri elements. Is that possible? I know in ANSYS Meshing is possible but, can I do it in ICEM CFD too?

 May 6, 2013, 03:31 #10 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 19 I think that works, but I wouldn't do that. I don't see any reason why you would try to get tri elements into a pipe. Hexa elements have the better quality anyway. Especially in pipes, where the flow is orthogonal to the faces most of the time. Also (nearly) everyone meshes a pipe like I show in picture no. 1. __________________ The skeleton ran out of shampoo in the shower.

 May 6, 2013, 03:59 #11 Senior Member   Javi Join Date: Jan 2013 Posts: 260 Rep Power: 8 Yes, youīre right. I always mesh the pipe in that way. But I ask this, because I need this form to make the mesh. Itīs better to me, to coupling with an turboīs shaft. So, I would like how to do this.

 May 6, 2013, 04:05 #12 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 19 Why don't you just post the complete geometry? That would cause less confusion... __________________ The skeleton ran out of shampoo in the shower.

 May 6, 2013, 04:27 #13 Senior Member   Javi Join Date: Jan 2013 Posts: 260 Rep Power: 8 I donīt have the geom. Itīs a case that I want to prove. A friend of mine asked me something similar the other day and I didnīt know how to respond to him. So, for that, Iīve asked it here. And because I would like to do a simple case like this mixing meshes.

 May 6, 2013, 04:34 #14 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 19 Alright! Good luck... __________________ The skeleton ran out of shampoo in the shower.

 May 6, 2013, 05:08 #15 Member   jeevan kumar Join Date: Mar 2009 Posts: 81 Rep Power: 9 You just merge the 4 vertices of the inside block of O-grid. The you will get what you wanted.

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